This invention relates to inspection continuously and without contact of a moving strip of material, in particular a strip of rubber intended for the manufacture of tires.
Such strips are produced by a machine such as an extruder associated with a die giving the desired shape to the rubber strip.
They must be inspected to detect variations of mass therein, notably air inclusions, which would render them unsuitable for the manufacture of tires.
Inspection by mechanical weighing has been tried, using a support roller for the moving strip. The efficacy and precision o this method of inspection, some hundredths in relative terms, are not really satisfactory. Furthermore, as the strip is carried away from the extruder by a mechanised belt, the pull tends to perturb the mechanical weighing.
Besides, it is not technically desirable to place the support roller for weighing very close to the extruder. In fact, the rubber strip emerges from it hot and deformable, at the same time moving around its mean position. Finally, precise and delicate adjustments are necessary each time that the dimensions of the strip are changed, according to the type of tire to be made.
In these circumstances, the object of the invention is to measure the mass per unit length of the moving rubber strip.
Equally, the object of the invention is to detect without contact very slight localised variations in weight, down to some thousandths in relative terms, of a moving strip of material.
The object of the invention is also to enable this precision to be maintained, even in the presence of displacements of the moving strip of material around its mean line of travel.
Another object of the invention is to effect said detection in difficult working conditions: the moving material still being hot on exit from the extruder; and a corrosive environment, with sulfur present.
Finally, it is an object of the invention to adapt the measurement easily to strips of different width and/or profile, corresponding for example to different types of tires to be made.